System configuration and control strategy for compound type hybrid excavator with ultra capacitor

This paper presents a power converter configuration for the compound type hybrid excavator with an ultra capacitor, which is directly connected in parallel to dc-link capacitor without DC/DC converter. With this structure, the efficiency of the system has been improved compared to the conventional compound type hybrid excavator where an ultra capacitor was connected via DC/DC converter. And, a power control strategy for the suggested configuration is described. To suppress the oscillation of the voltage of the ultra capacitor, an observer for the internal voltage of the ultra capacitor is devised. To evaluate the effectiveness of the proposed configuration and power control strategy, extensive computer simulations have been performed and the results are discussed. The feasibility of the simulation results is experimentally verified based on mid-sized excavator.